This invention relates to a scanning optical device comprising at least a light source, a collimator lens into which a light beam emitted from said light source enters, a deflector which deflects the light beam having passed said collimator lens to the direction of main scanning, and an image forming lens which focuses the light beam having passed said deflector on the surface to be scanned and to an image forming apparatus having a plurality of the above-mentioned scanning optical devices arranged in the direction of sub-scanning.
Generally speaking, in an image forming apparatus capable of forming a multi-color image, a cylinder-shaped, or belt-shaped image bearing member is used. In forming a multi-color image by using this image bearing member, charging, exposure and development are carried out for each of colors with the image bearing member rotated (moved), and the multiple color toner images are superposed one after another on the image bearing member and transferred onto a sheet of transfer paper by a one-time transfer operation.
Incidentally, in order to accomplish a high-speed printing, it is required not a structure such that exposure processing (writing by light) for one color is carried out in every rotation of the image bearing member but a structure such that the exposures for all of four colors Y, M, C, and K are carried out in every rotation of the image bearing member. In this case, not only a plurality of the developing units but also a plurality of the scanning optical devices corresponding to the respective colors should be provided in order that the multiple exposures and developments should be done at different positions on the image bearing member.
For example, in the case where a color image is formed using the four colors Y (yellow), M (magenta), C (cyan), and K (black), the scanning optical devices and the developing units for the respective colors Y, M, C, and K are arranged in the direction of sub-scanning, and each of the scanning optical devices is let to form the latent electrostatic image of the color corresponding to it in such a manner as to form the toner images precisely superposed on one another, and the latent electrostatic images are developed.
In this case, to remark one pixel of the latent images formed by the respective scanning optical devices, if the position of this pixel is deviated for a certain color, synthesis of the color can not be done at this pixel portion, producing a color deviation and lowering resolution, and image quality is deteriorated. In order to prevent the occurrence of this color deviation and the lowering of resolution, it is required that not only the characteristics of the respective scanning optical devices are made to be the same so as to be able to write the same scan line, but also the respective optical devices are fixed in a precise positional relationship so as to make the scan lines for the respective colors coincide with one another.
To consider the characteristics of the scanning optical device as an individual one, it is desirable for obtaining a good image that the scan lines on the surface to be scanned are straight and, at the same time, the arrangement of the pixels forming any one of the scan lines has a uniform interval between any adjacent pixels. However, actually, the positioning of optical parts etc can not be precisely performed, therefore, there have been problems that scan lines on the surface to be scanned are curved and that the arrangement of the pixels forming a scan line has an uneven interval between pixels.
Further, in the case where a multi-color image is formed, there has been a problem that the characteristics of the respective scanning optical devices can not be made equal, neither the respective scanning optical devices can be fixed in a precise positional relationship, resulting in deterioration of image quality.
This invention has been made in order to solve the above-described problems, and it is an object of this invention concerning a scanning optical device to actualize a scanning optical device capable of adjusting the scanning beam easily.
Further, it is an object of this invention concerning an image forming apparatus to actualize an image forming apparatus capable of getting rid of the deterioration of image quality owing to the scanning optical device.
The above object can be attained by the following structures.
A scanning optical system, comprises:
a plurality of scanning optical devices, each scanning optical device including
a light source to emit a light beam,
a collimator lens into which the light beam emitted from the light source enters,
a deflector to deflect the light beam passing through the collimator lens in a main scanning direction,
an image forming lens to focus the light beam coming from the deflector onto a scanned surface, and
a base plate on which the light source, the collimator lens, the deflector and the image forming lens are fixed, wherein the plurality of scanning optical devices are piled up in a sub-scanning direction perpendicular to the main scanning direction in such a manner that each base plate is substantially parallel to other base plates; and
a plurality of link members to connect two neighboring base plates independently of other base plates.
A scanning optical system, comprises:
a plurality of scanning optical devices, each scanning optical device including
a light source to emit a light beam,
a collimator lens into which the light beam emitted from the light source enters,
a deflector to deflect the light beam passing through the collimator lens in a main scanning direction,
an image forming lens to focus the light beam coming from the deflector onto a scanned surface,
a contact member to come in contact with a first side surface of the image forming lens at three contact points on both end portions and a middle portion of the first side surface in terms of the main scanning direction;
a pressing member to come in pressure contact with a second side surface of the image forming lens so as to press the image forming lens toward the contact member and
a base plate on which the light source, the collimator lens, the deflector, the image forming lens, the contact member and the pressing member are fixed, wherein the plurality of scanning optical devices are piled up in a sub-scanning direction perpendicular to the main scanning direction in such a manner that each base plate is substantially parallel to other base plates; and
a plurality of link members to connect two neighboring base plates independently of other base plates.
A scanning optical device, comprises:
a light source to emit a light beam;
a collimator lens into which the light beam emitted from the light source enters;
a deflector to deflect the light beam passing through the collimator lens in a main scanning direction;
an image forming lens to focus the light beam coming from the deflector onto a scanned surface;
a contact member to come in contact with a first side surface of the image forming lens at three contact points on both end portions and a middle portion of the first side surface in terms of the main scanning direction; and
a pressing member to come in pressure contact with a second side surface of the image forming lens so as to press the image forming lens toward the contact member.
Further, the above object can be attained by the following preferable structures.
This invention concerning a scanning optical device is the one comprising at least a light source, a collimator lens into which a light beam emitted from said light source enters, a deflector which deflects the light beam having passed said collimator lens to the direction of main scanning, and an image forming lens which focuses the light beam having passed said deflector on the surface to be scanned, said scanning optical device further comprising contact members capable of being in contact with said image forming lens at three points, that is, the both end portions of said image forming lens in the direction of main scanning and an intermediate point between the both end points respectively at the time of adjusting the position of said image forming lens, and an urging means for urging said image forming lens toward said contact members.
In this invention, a mechanism for adjusting and determining the position of the image forming lens is provided. The image forming lens is positioned in the vicinity of the surface to be scanned, and is easy to have a bend owing to its long size. In spite of this, according to this invention for adjusting the position to fix this image forming lens, the scanning beam is corrected easily and with a good efficiency. In addition to it, because the image forming lens is in contact with the contact members at the three points, namely, the both end portions in the main scanning direction and an intermediate portion between the both end portions at the time of adjusting the position of the image forming lens, it is possible to let the image forming lens take any position by displacing the points of contact.
In this case, if the points of contact of the image forming lens at its both end portions in the main scanning direction with the contact members are made to be positioned on a straight line which is approximately parallel to the main scanning direction, and the point of contact at the intermediate portion is placed at a position deviated from a position on the above-mentioned straight line in the direction perpendicular to the surface to be scanned, the adjustment of position of the image forming lens can be performed by moving at least one of the contact members placed at the above-mentioned three points of contact in the direction of sub-scanning.
It is desirable that the image forming lens is fixed to the base in order to prevent the deviation of the position of the image forming lens, after the adjustment and determination of the position of the image forming lens. By carrying out this fixing at a position in the neighborhood of the point of contact at the intermediate portion of the image forming lens, the image forming lens is fixed only at the intermediate portion, which makes it possible for the image forming lens to expand and contract freely in accordance with the variation of temperature and humidity of the surrounding; thus the image forming lens is never bent unnaturally and it can be avoided the unfavorable influence that a complex bending etc are produced in the scan lines.
This invention concerning an image forming apparatus is the one having a plurality of scanning optical devices arranged in the direction of sub-scanning, each of said scanning optical devices comprising at least a light source, a collimator lens into which a light beam emitted from said light source enters, a deflector which deflects the light beam having passed said collimator lens to the direction of main scanning, and an image forming lens which focuses the light beam having passed said deflector on the surface to be scanned, wherein any pair of the neighboring scanning optical devices are linked to each other, and the linking between these scanning optical devices is made by fixing a link member to each of the scanning optical devices in a manner capable of taking off, the position of one of the neighboring scanning optical devices being determined in the state of being freely movable (hereinafter referred to as xe2x80x98state of floating offxe2x80x99) against the other, and after that, fixing said linking members of the neighboring scanning optical devices to one another.
According to this invention, the positions of a plurality of scanning optical devices arranged in the direction of sub-scanning are adjusted and determined in the state of floating off against the others, and the linking members are mutually linked after determining the positions. Owing to this, by once precisely adjusting and determining the positions of the respective scanning optical devices, the positional relationship among the scanning optical devices will never be varied after that, and the deterioration of image quality owing to the scanning optical device can be prevented.
Further, because the linking members are fixed to the respective scanning optical devices in a manner capable of being taken off, in the case where the determination of the positions is proved to be not satisfactory after the linking of the neighboring scanning optical devices, it is possible that these link members are taken off from the scanning optical devices, with the state of mutual linking of the link members let to remain as it is, and then a new link members are attached to the scanning optical devices, and the positions are determined again, and the new link members are fixed to one another. Owing to this, it has become possible to utilize again the scanning optical devices.
Another invention concerning an image forming apparatus is the one having a plurality of scanning optical devices arranged in the direction of sub-scanning, each of said scanning optical devices comprising at least a light source, a collimator lens into which a light beam emitted from said light source enters, a deflector which deflects the light beam having passed said collimator lens to the direction of main scanning, and an image forming lens which focuses the light beam having passed said deflector on the surface to be scanned, wherein each of said scanning optical devices comprises contact members capable of being in contact with said image forming lens at three points, that is, the both end portions of said image forming lens in the direction of main scanning and an intermediate point between the both end points respectively at the time of adjusting the position of said image forming lens, and an urging means for urging said image forming lens toward said contact member, and further, any pair of the neighboring scanning optical device are linked to each other, and the linking between these scanning optical device is made by fixing a link member to each of the scanning optical devices in a manner capable of taking off, the position of one of the neighboring scanning optical devices being determined in the state of floating off against the other, and after that, fixing said linking members of the neighboring scanning optical devices to one another.
According to this invention, in each of the scanning optical devices, the scanning beam can be corrected easily and with a good efficiency. Further, because the linking members are mutually linked after determining the positions, the positional relationship among the scanning optical devices is never varied, and the deterioration of image quality owing to the scanning optical device can be prevented. Furthermore, reutilization of the scanning optical device has become possible.
If an adhesive of the UV-hardening type is used for the above-described fixing of the scanning optical devices to one another, the determination of the positions is carried out with the adhesive injected into every clearance between the linking members, and the fixing can be done by applying an ultraviolet ray immediately after the determining of the positions, which makes the linking operation easy.